Color kinescope utilizing x-rays



Dec. 20, 1955 1. J. HEGYI COLOR KINESCOPE UTILIZING X-RAYS 2Sheets-Sheet 1 Filed Jan. 30 1951 INVENTOR Imge JI MM Hag 1' a .9

ORNEY United States Patent COLOR KINESCOPE UTILIZING X-RAYS Imre J.Hegyi, Lawrenceville, N. J., assignor to Radio Corporation of America, acorporation of Delaware Application January 30, 1951, Serial N 208,615

Claims. 01. 313-92 This invention relates to improvements in multi-colorkinescopes for use in television and other systems for the communicationof intelligence. In particular, it relates to a novel and improvedtarget assembly for use in such kinescopes.

In certain types of color kinescopes, notably of the masked targetvariety, the colored light emissive areas of the screen are ofsub-elemental visual dimensions and must be maintained in exactalignment with the apertures of the masking screen. This gives rise toserious manufacturing problems.

Accordingly, one object of the present invention is to provide a colorkinescope which is free of alignment problems and therefore easier tomanufacture.

Another object is to provide an improved kinescope wherein it is notnecessary to lay down the phosphor target in discrete sub-visual areas.

Another object is to utilize X-rays as phosphor excit ing agents in akinescope.

The present invention is predicated on the fact that certain phosphormaterials will absorb X-rays of one frequency and remain relativelyinsensitive to X-rays of other frequencies, and on the further fact thatwhen these X-rays are absorbed the absorbing medium emits electrons.(Cf. X-Rays in Theory and Experiment, Compton and Allison, pp. 17, 526if.) By using different color producing phosphors as the absorbingmedium a multicolor kinescope is provided. The phosphors are blendedinto a mixture and need not be laid down in discrete areas.

In a preferred embodiment, a high velocity cathode ray beam bombardsmetallic targets to produce X-rays. These X-rays are then selectivelyfiltered and directed toward the phosphor mixture. The differentphosphors produce different colors as they are excited by the differentfrequencies of X-rays and a full color image results.

The invention is more completely described in connection with theaccompanying two sheets of drawings in which:

Fig. 1 is a longitudinal section of a kinescope embodying a preferredform of the invention;

Fig. 2 is a plan view along the line 22 of Fig. 1 showing the targetelements of the screen and the electrical connections thereto;

Fig. 3 is a cross section of an alternative screen structure inaccordance with the invention;

Fig. 4 is a cross section of still another screen structure embodyingthe invention; and

Fig. 5 is a graph showing the X-ray spectrum resulting from bombardmentof a tungsten target by different electron beam velocities. It will bereferred to in the explanation of the invention.

The tube of Fig. 1 comprises an evacuated envelope 11 having a neckportion 13 and a main chamber 15. The neck portion 13 contains anelectron source or gun comprising an electron emitter 14 and a controlelectrode 16. The electron beam 17 is directed into the main chamberwhere it bombards a target or screen 19. The target 19, in the instantcase, is supported upon the inner surface of the glass face plate orwindow 21 of the tube. It comprises a layer 23 of phosphor materialswhich are 'ice sensitive to X-rays, a layer of metallic elements 25, 27,29 which produce X-rays of different characteristic frequencies whenbombarded by electrons, and a layer of filter elements R, G, B whichpermit the passage of X-rays of certain frequencies and block thepassage of X-rays of other frequencies. The phosphor 23 is laid down onthe face plate 21 and the filters R, G, B and metal strips 25, 27, 29are superimposed on the phosphor by spraying through a screen, or in theform of individual strips of thin metal ribbon. The face plate 21 may beconstituted of a lead glass to prevent X-rays from emanating from theface of the tube.

The layer 23 is a mixture of three different phosphors. Each of thesephosphors is sensitive to a given frequency of X-rays and relativelyinsensitive to X-rays of other frequencies. Another characteristic ofthese phosphors is that when one of them is excited by X-rays of thefrequency to which it is sensitive it emits red light. Another, insimilar fashion emits green light; and the third, blue light. Examplesof phosphors which possess these characteristics are: cadmium sulfidefor red light, manganese activated zinc silicate for green light andcalcium tungstate for blue light. These difierent phosphors need not belaid down in discrete areas of sub-visual dimensions as is necessarywith the phosphor targets in most multi-color kinescopes. Instead, theyare mixed together and settled upon the face plate 21 in a singlecoating. The different colors in the output from the tube are the resultof the individual phosphors within the mixture being excited by theparticular frequency of X-ray to which they are sensitive and radiatingtheir characteristic colors.

In order to produce the different X-ray frequencies which will excitethe different phosphors it is necessary first, to determine to whatfrequency of X-rays each of the color producing phosphors is sensitive;and then, to devise a means for bombarding the phosphor layer 23 withX-rays of these different frequencies in a selective manner controlledby color input signals.

The frequency to which the individual phosphors are sensitive may bedetermined from Tables of Emission and Absorption Wavelengths for thevarious elements involved. One such table is offered by M. Siegbahn inSpektroskopic der Rontgenstrahlen, 2nd edition, Springer, Berlin 1931;and reprinted in Structure of Metals, by C. S. Barret, McGraw-Hill, asAppendix II on page 516.

Since only the absorbed X-rays cause excitation, by determining the Kabsorption edge frequency (which is the frequency of maximum absorption)for a particular phosphor one can find to what frequency that phosphoris sensitive. The absorption edge is a wavelength above which there isminimum absorption by the element and below which there is maximumabsorption. In cases where the phosphor is a compound of severalelements, the absorption edge of the element having the highest atomicnumber (i. e. the lowest absorption edge) is controlling. It is alsoconvenient to note that the absorption edge of an element decreases asits atomic number increases.

Applying these principles and using the tables identified above it isfound that the three phosphors proposed have the following absorptionedges:

Calcium Tungstate (CaWOa) (Blue) A 0.178

(The element having the highest atomic number in each of the abovephosphor compositions has been underlined for facility in consulting thetables.)

It nowbecomes evident that to activate the red phosphor X-rays ofapproximately 0.46 A. are needed, to activate the green X-rays ofapproximately 1.28 A. are needed, and to activate the blue approximately0.178 A. In order to obtain these frequencies it is advantageous toselect for the metal strips 25, 27, 29 materials which when bombarded byelectrons produce their strongest radiations in the proper portion ofthe X-ray spectrum. The same tables employed above are useful here. Thistime, check under the emission line and use the Km emission because itis the strongest radiation. From this operation the followingcombinations are obtained:

With this information, it is now possible to make the may be separatedfrom each other by insulating material in order to keep the propervoltages on the proper strip and to keep stray electrons from bombardingthe phosphor material 23 between the strips 25, 27, 29 if the scanningelectron beam falls out of register with the metal targets.

In order to eliminate X-rays of undesired or spurious frequencies andmake the color response of the kinescope more selective, filter elementsR, B, G are interposed between the metallic elements 25, 27, 29 and thephosphor layer 23. The filter materials are selected by reference to thepreviously identified Tables of Emission and Absorption Wavelengths withthe end in view of placing in the path of the X-rays an element with anabsorption edge lower than the frequency which the particular metalstrip 25, 27, 29 is supposed to provide for radiation of its particularcolor phosphor. This results in absorption of any X-rays below thecritical frequency which might be present at low levels along with thecharacteristic Km radiation of the metal strip bombarded. For thephosphors and targets previously suggested, the following filters may beused:

Color De- Absorption Kn: Emis- Absorption sued Phosphor Edge, A MetalTarget 510m, Filter Edge, A.

red OdS O. 46 Sb 0. 47 Indium (In)... 0. 44 green ZnSiOr l. 28 Ge 1. 25Gallium (Ga) 1. 19 blue CaWO; O. 178 An 0.18 Osmium (Os). 0.167

metal strips 25 of antimony so that their X-rays will excite the redphosphor ('CdS), to make the metal strips 27 of germanium to excite thegreen phosphor (ZnSiOt), and to make the strips 29 of gold to excite theblue phosphor (CaWOs).

Once the material of the strips 25, 27, 29 is decided upon, however, theproblem of adequate radiation in the desired portion of the X-rayspectrum is not entirely solved. A metallic element will not produceX-rays of a given frequency, even ifits K radiation predominates in thatfrequency, unless it is bombarded by electrons of the proper velocity.The book Structure of Metals referred to above discusses this problem onpp. 46 if. and proposes the formula m'in.

for determining the shortest wave, length of 'X-rays which will beemitted when a metal target is bombarded, by electrons of a givenvelocity.

Since in. his Case ex v length of X-ray desired is, n n, h ec s y ltagan'be det rmined by nverting the a ov f rmula into:

In this manner the following values for V are found:

Fig. 2 shows a plan view in schematic fashion of a method whereby theproper voltages are applied to the various metal strips 25, 27, 29 toinsure that the electron beam 17'strikes them with the proper velocity.As shown, the strips 25, 27, 29 are superimposed on the filter strips R,B, G whichlay directly on the phosphor and run across the entire faceplate 21 of the tube. They could, however, be limited to the rectangulararea in the center where the picture is customarily presented. The metalstrips 25, 27, 29 may be spaced apart asshown, or they In order to makethe phosphor response more monochromatic the target arrangement shown inFig. 4 may be used. Here, in addition to a filter R, G or B as explainedabove, there is inserted between the X-ray productive metal strip 25,27, '29 and the phosphor screen 23 a second filter R, G, or B. Thesecond filter element is selected from the same tables and has anabsorption edge above the Km emission line of the metal strip 25, 27, 29with which it is associated. The result is what is known in the X-rayart as a Ross Filter the operation of which is explained in the bookStructure of Metals cited above, at page '57 ii, in the Proceedings ofthe National Academy of Science, vol. 14 (1928) at page 20 ii, and inthe Review of Scientific Instruments, vol. 10 (1939) at page 186 if. Theefiect is to produce a strong monochromatic X-ray beam of a frequencybetween theabsorption edges of the two filters.

Another feature of the target shown in Pig. 4 is a single sheet of metal31 in the place of the individual strips 25,, 27, 29. This metal sheet31 .is selected from one of the higher .atOmic, numbers so that it willproduce radiation across the desired portion of the X-ray spectrum,Tungsten is suggested but other metals with similar characteristics may0ev Used. Consultationtof the chart on page 45 of Structure of Metals(cited above), and reproduced as Fig. 5 of the drawings, shows thatelectrons bombarding a tungsten target above '70 ltv. will produceX-rays across the frequency spectrum necessary to excite the phosphorsused in the proposed color kinescope. It should be noted that the solidline curves are the exact reproduction of the graph presented inStructure of Metals and the values are taken, from experiments performedby Ulrey. The dotted line covering the kv. situation, however, is anextrapolation added to the original graph to suit the needs of theproposed kincscope. The leading edge of the extrapolated curve waslocated by the formula min. A.

which has, been referred to above. 7 7

Another form of target is shown in Fig. 3. Here, the metal strips 25,27, 29 act as their own filters. The electrons hit the back of thetarget and the resulting X-rays must travel through the target materialbefore they strike the phosphor layer 23. Since the Km emission isalways of a higher frequency than the absorption edge of the targetmaterial, the thickness of the targets 25, 27, 29 may be so controlledthat they themselves act as filters. The target materials are chosen asabove so that their X-ray radiation is predominately in the region ofthe absorption edge of the phosphor.

The tube 11 as shown in Fig. 1 has only eleven target elements 25, 27,29 running across its face. Actually, there should be many times thisnumber. The invention is being demonstrated as used in a line sequentialtele ision system and there should be at least as many target elementswith their associated filters R, G and B as there are raster lines inthe particular system employed. Since the color lines are fixed by thefilter elements R, G and B and each visual line may be made up ofsub-elemental red, green and blue lines, a line sequential system mightuse as many as 1575 different target elements 25, 27, 29 with associatedfilters R, G and B to give each one of the 525 visual elemental linesits full color complement. A lesser number may be used with a consequentloss in image definition.

As shown in Fig. 1 the cathode ray beam 17 is caused to scan each of thetarget elements 25, 27, 29 successively through the action of thedeflection coils 33. In order to assure perfect registry of the beam 17with the target strips 25, 27 29 any of the beam-to-line registrydevices known to the color television art may be employed. An example isthe control grille claimed in copending U. S. application of H. B. Law,Ser. No. 181,342, filed August 25, 1950; now U. S. Patent 2,602,145.

It should also be borne in mind that, although the invention has beendescribed with reference to a line sequential system, it can be operatedin a field sequential manner by scanning all of the lines productive ofthe same color in a single sequence. Or, it may be employed in anelement sequential system if the targets and filters are laid down indots instead of in lines. In any of these applications it will provide acolor kinescope target assembly wherein all of the phosphor material islaid down in a single coating without any necessity for division intodiscrete sub-visual areas; and, furthermore, one in which the additionaltarget structure may be superimposed directly on the phosphor materialwithout any problem of mechanical alignment of phosphor elements with ashadow mask.

What is claimed is:

1. A luminescent screen electrode for a color kinescope comprising alight emissive layer constituted of a mixture of phosphor materials eachcapable of emitting light of a characteristic color when bombarded byX-rays of a particular frequency; said mixture of phosphor materialscomprising CaWOs, CdS, and manganese activated ZnSiOt.

2. A cathode-ray device comprising an evacuated envelope containing anelectron beam source and a target assembly, said target assemblycomprising a layer of metal which will produce X-rays of a givenfrequency when bombarded by an electron beam, and a layer of phosphormaterial which luminesces when bombarded by X-rays of said givenfrequency.

3. The invention according to claim 2 and wherein said metallic elementsproductive of said different characteristic frequencies are of differentphysical dimension with reference to the path of said X-rays toward saidphosphor layer.

4. A multi-color kinescope comprising an evacuated envelope having anelectron beam source in one part thereof and a target electrode inanother part thereof, said target electrode comprising a mixture ofdifferent phosphor materials, each of said difierent phosphor materialsbeing predominately sensitive to X-rays of a characteristic wave lengthand emissive of a characteristically colored light when bombarded byX-rays of that wave length, means interposed between said electron beamsource and said target electrode for converting electrons from saidsource into X-rays of said critical wave lengths.

5. In a color kinescope the combination of means for producing X-rays ofdifferent wave lengths with a target electrode comprising a mixture ofphosphor materials, different ones of the phosphor materials of saidmixture being predominately sensitive to only X-rays of a given one ofsaid different wave lengths.

6. The invention according to claim 5 and wherein said layer of metal isproductive of a given band of X-ray frequencies, said phosphor layercomprises a mixture of different phosphors sensitive to difierentfrequencies within said given band, and said first and second layers ofX-ray filter elements comprise discrete filters within each layer,different ones of said discrete filters of said first layer having theirK absorption edge lower than the K absorption edges of given ones ofsaid different phosphors, and different ones of said discrete filters ofsaid second layer being in physical register with said ditferent filterelements of said first layer in paired fashion and having an atomicnumber lower than the phosphor having a higher K absorption edge thanthe filter of said first layer with which the filter of said secondlayer is paired.

7. A cathode ray device comprising an evacuated envelope containing: anelectron gun; a metallic target in the path of electrons from said gun,said target being productive of X-rays when bombarded by electrons; alayer of X-ray filtering material which passes only given X-rayfrequencies; and a layer of phosphor material sensitive X-rays of saidpassed frequencies.

8. A multi-color kinescope comprising an evacuated envelope containingan electron beam source and a target assembly located in the path of theelectron beam from said source, said target assembly comprising: a layerof electrically separate metallic elements, different ones of saidmetallic elements being productive of X-rays of different characteristicfrequencies when bombarded by elec trons; and a layer of phosphormaterial, said layer comprising a mixture of different phosphors whichare sensitive to difierent ones of said characteristic frequencies.

9. A target assembly for a cathode ray tube comprising a layer of metalcapable of producing X-rays of a given frequency distribution whenbombarded by electrons and a layer of phosphor material sensitive toX-rays of said frequency, interposed between said metal and phosphorlayers a first layer of X-ray filter elements with a K absorption edgelower than said frequency, and a second layer of X-ray filter elementshaving an atomic number lower than said phosphor.

10. In a multi-color kinescope the combination of a metal target, meansfor bombarding said metal target With high velocity electrons to produceX-rays, an X-ray sensitive screen, including a mixture of phosphorshaving different atomic numbers, in the path of X-rays from said target,and a plurality of combinations of X-ray filter elements interposedbetween said target and said screen, each of said combinationscomprising a filter element having an atomic number higher than, and afilter element having an atomic number lower than, the atomic number ofone of the phosphors of said mixture.

References Cited in the file of this patent UNITED STATES PATENTS1,973,886 Scanlan et al. Sept. 18, 1934 2,442,961 Ramberg June 8, 19482,452,522 Leverenz Oct. 26, 1948 2,452,523 Leverenz Oct. 26, 19482,508,098 Chilowsky May 16, 1950 2,509,766 Gross May 30, 1950 2,546,160Lengyel Mar. 27, 1951 2,559,279 Charles July 3, 1951 2,644,096 Fine June30, 1953 FOREIGN PATENTS 276,678 Great Britain Nov. 3, 1927

